Underwater pelletizers which produce a pelletized product in the form of a slurry of pellets and water are well known for many years in the pelletizing industry as well as in patents of the assignee from as early as U.S. Pat. No. 4,123,207 issued Oct. 31, 1978. Centrifugal dryers are also well known in the prior art and have been disclosed by the assignee as early as U.S. Pat. No. 3,458,045 issued Jul. 29, 1969, and more recently in U.S. Pat. Nos. 5,265,347 (issue date Nov. 30, 1993), 6,237,244 (issue date May 29, 2001), 6,739,457 (issue date May 25, 2004), and 6,807,748 (issued Oct. 26, 2004). Details of these patents are included herein, in whole or in part, by way of reference.
The centrifugal pellet dryers in the prior art satisfactorily dry plastic particles, and particularly plastic pellets when properly operated. However, existing dryers have areas in which the plastic pellets and particles, and particularly plastic flakes, being dried, become lodged, form occlusions, or otherwise, accumulate. These areas are generally known as hang-up points in which pellets or plastic flakes or particles remain after a drying cycle has been completed. The pellets, flakes or particles lodged in various hang-up points may present a contamination problem in sequential drying cycles even when the same pellet slurry is supplied to the dryer.
Of more significant concern, a centrifugal dryer is commonly used to dry different plastic particles during sequential drying cycles. When a subsequent drying cycle is drying plastic particles different from those in a previous drying cycle, some of the particulates of the previous drying cycle that have been lodged in the hang-up points will be entrained in and mixed with different plastic pellets, flakes, or particles being dried in a subsequent drying cycle. This circumstance results in contamination of the plastic particles being dried in the subsequent drying cycle by those retained in the hang-up points during a previous drying cycle.
The build-up of plastic particles during water conveyance or processing may lead to hang-up points in other parts of the system other than the dryer, or may restrict flow through the system by clogging or occlusion, and may lead to downstream contamination where plastic particles are released from the hang-up points, clogs or occlusions, periodically and unpredictably.
The present invention is a self-cleaning dryer, water-conveying system and/or water processing system and a method of use which overcome the problems of hang-up points in prior art dryers as well as in the water conveying and processing systems similarly contaminated by hang-up points and occlusions by eliminating the particulate build-up from the hang-up points, clogs, and occlusions. Thus, contamination of plastic pellets, flakes or particles being dried in a drying cycle by residuals retained in various hang-up points, clogs, or occlusions during a previous drying cycle in which different particulates were processed is avoided.